SUMMARY/ABSTRACT Gastric adenocarcinoma is the second most common cause of cancer related-death worldwide. Recent estimates indicate 900,000 cases were recorded in 2002 with 700,000 deaths [1, 2]. Overall, in the U.S., relative 5-year survival rates are less than 20%. Patients are usually diagnosed with gastric cancer in their 6th decade of life. Infection with H.pylori, a class I carcinogen according to WHO classification, is the main risk factor. Chronic H.pylori infection, especially with CagA+ strains, persists for several decades before the development of gastric cancer. A key question that remained unanswered, in the context of gastric cancer, is the fact that infection with H.pylori starts at childhood whereas gastric cancer, when develops, occurs after several decades of chronic infection. Understanding the molecular events that enhance and promote H.pylori mediated carcinogenic effects has significant contribution to our knowledge of the biology of the disease, early diagnosis, and potential preventive and therapeutic strategies of gastric cancer. We have developed an innovative hypothesis to investigate the role of trefoil factor 1 (TFF1) in protecting against H.pylori-induced inflammation and oncogenic signaling that lead to the development of gastric cancer. This hypothesis is supported by strong preliminary data from human tissues, animal models of gastric cancer, and in vitro studies that demonstrate; 1) H.pylori infection of gastric mucosa persists for several decades before the development of gastric cancer; 2) TFF1 protects epithelial cells against chronic inflammation and activation of pro- inflammatory and oncogenic signaling; 3) the loss of TFF1 in human gastric cancer coincides with early stages of gastric cancer development; intestinal metaplasia and dysplasia, 4) TFF1 knockout (KO) mice develop a cascade of: spontaneous chronic inflammation in gastric mucosa ` low grade dysplasia ` high grade dysplasia ` gastric cancer. In this proposal, we will utilize the TFF1 KO mouse model, in vitro approaches, and de-identified human tissue samples to gain knowledge about the role TFF1 expression in the multi-step gastric carcinogenesis. In aim 1, we will examine the role of TFF1 in abrogating H.pylori-induced gastric tumorigenesis with special emphasis on inflammation mediated tumorigenesis. In aim 2, we will investigate the role of TFF1 in modulating oncogenic signaling. We will investigate the mechanistic interplay between TFF1- loss, inflammation, and H.pylori. We will also determine the clinical and histopathological value of the relationship between TFF1-loss and expression of NF-kB and b-catenin in well-defined stages of gastric cancer development in de-identified human gastric tissue samples. In Aim 3, we will perform comprehensive analysis of the methylome and transcriptome in the TFF1 KO mouse model, at well-defined histological stages, in presence of H.pylori. This will be followed by powerful integrated Mouse to Human bioinformatics, network analysis and validation using our database of human gastric cancer. We will also investigate the interplay between TFF1-loss, inflammation, methylation and H.pylori infection to determine the causal relationship between these factors and DNA methylation. Upon completion of this proposal, we expect to gain more understanding of the role of TFF1-loss in shaping the H.pylori-induced inflammation and carcinogenic signaling in the multistep gastric tumorigenesis. Our results will have a strong impact on our knowledge of the biology and molecular basis of the development of gastric cancer. The findings could have a potential role in the preventive, early diagnosis, and possibly therapeutic interventions in this disease. In our opinion, the proposed studies present a novel direction that will advance the field and add to our present knowledge of the biology and molecular basis of gastric carcinogenesis.